- canvas fills the entire screen on any device; the 480x640 world is
scaled to fit and bottom-aligned so the ground always sits on the
bottom edge, with the sky painted full-bleed behind it
- the canvas buffer now always matches its laid-out size, so the drawing
can never drift out of step with the screen
- HUD (score, badge, buffs, toasts, biome banner) moved to screen space
so it stays pinned to the real screen edges
- sun and stars drawn in screen space so the sky above the play area is
not empty
- PWA: manifest, service worker (offline), generated app icons and an
in-game INSTALL APP button
- overlays now dim the whole screen, not just the game strip
